Numerous protective layers for metallic components that are supposed to increase the corrosion resistance and/or oxidation resistance of said components are known from the prior art. Most of these protective layers are known under the collective name MCrAlX, where M stands for at least one of the elements selected from the group consisting of iron, cobalt and nickel and further essential constituents are chromium, aluminum and yttrium.
Typical coatings of this type are known from U.S. Pat. Nos. 4,005,989 and 4,034,142.
The addition of rhenium (Re) to NiCoCrAlY alloys is also known.
The objective of increasing the inlet temperatures of both stationary gas turbines and aircraft engines is of considerable significance in the specialist field of gas turbines, since the inlet temperatures are important variables determining the thermodynamic efficiencies which can be achieved by gas turbines. The use of specially developed alloys as base materials for components which are to be exposed to high thermal stresses, such as guide vanes and rotor blades, and in particular the use of single-crystal superalloys, allows the use of inlet temperatures of well over 1000° C. Nowadays, the prior art permits inlet temperatures of 950° C. and above in the case of stationary gas turbines and 1100° C. and above in the case of gas turbines for aircraft engines.
Examples of the structure of a turbine blade or vane having a single-crystal substrate, which for its part may be of complex structure, are revealed by WO 91/01433 A1.
Whereas the physical load-bearing capacity of the base materials which have by now been developed for the highly stressed components does not present any major problems with a view to possible further increases in the inlet temperatures, protective layers have to be employed to achieve sufficient resistance to oxidation and corrosion. In addition to the sufficient chemical stability of a protective layer under the attacks expected from flue gases at temperatures of the order of magnitude of 1000° C., a protective layer also has to have sufficiently good mechanical properties, not least with a view to the mechanical interaction between the protective layer and the base material. In particular, the protective layer must be sufficiently ductile to enable any deformation of the base material to be followed and not to crack, since points of attack for oxidation and corrosion would be created in this way.
Accordingly, the invention is based on the object of providing an alloy and a protective layer which has a good high-temperature stability with regard to corrosion and oxidation, good long-term stability and, moreover, is particularly well matched to mechanical stresses which are expected at a high temperature in particular in a gas turbine.
The object is achieved by a layer system,    at least comprising:    a substrate,    an at least two-layered metallic layer    consisting of at least a first bottom layer and    a second top layer on the bottom layer,    wherein the bottom layer    comprises an MCrAlX alloy    without tantalum (Ta) and without silicon (Si) and without iron (Fe),    in particular contains at least the following elements,    very particularly consists thereof:    (amounts in % by weight):    22%-26% cobalt (Co),    12%-16% chromium (Cr),    10%-12% aluminum (Al),    0.20-0.60,    nickel,    in particular remainder nickel,    wherein the second layer comprises an MCrAlX alloy,    either with tantalum (Ta) and/or iron (Fe)    or with the γ and the γ′ phase and optionally the β phase,    where X is optional and is at least one of the elements from the group comprising scandium, rhenium and the rare earth elements,    in particular yttrium (Y).
Further advantages are achieved by:                the alloy of the bottom layer (7) contains 24%-26% cobalt (Co);        the alloy of the bottom layer (7) comprises 22% to 23.5% cobalt;        the bottom layer (7) contains 15%-16% chromium (Cr);        the bottom layer (7) contains 12%-14% chromium (Cr);        the bottom layer (7) contains 0.3%-0.5% yttrium (Y);        the alloy of the bottom layer consists of cobalt (Co), chromium (Cr), aluminum (Al), yttrium (Y) and nickel (Ni);        the content of tantalum (Ta) in the alloy of the top layer is between 0.1% by weight and 7.0% by weight,                    in particular is 1% by weight;                        the proportion of tantalum (Ta) in the alloy of the top layer is at least 2.0% by weight,                    in particular is between 3.0% by weight and 6.0% by weight;                        the proportion of tantalum (Ta) in the alloy of the top layer is between 4% by weight and 8% by weight,                    in particular is 5% by weight-7% by weight, very particularly is 6% by weight;                        the content of cobalt (Co) in the alloy of the top layer is at least 1% by weight;        the alloy of the top layer comprises at least 1% by weight chromium (Cr);        the alloy of the top layer (10) comprises 15% by weight-16% by weight chromium (Cr), in particular 15.5% by weight Cr;        the alloy of the bottom layer comprises no rhenium (Re);        the content of aluminum (Al) in the alloy of the top layer is between 5% by weight-15% by weight,                    in particular is between 8% by weight-12% by weight;                        the content of aluminum (Al) in the alloy of the top layer (10) is between 10.5% by weight-12% by weight,                    in particular is 11.5% by weight;                        the alloy of the top layer comprises no rhenium (Re);        the following holds true for the alloys of the metallic layers:                    not containing zirconium (Zr) and/or            not containing titanium (Ti) and/or            not containing gallium (Ga) and/or            not containing germanium (Ge);                        the alloy of the bottom layer and/or of the top layer contains no silicon (Si);        the alloy of the top layer lies between 22% by weight and 26% by weight,                    in particular lies between 24% by weight and 26% by weight;                        the alloy of the top layer (10) comprises at least 1% by weight chromium (Cr);        the alloy of the top layer is nickel-based;        the alloy of the bottom layer is nickel-based;        the top layer comprises the γ phase, the γ′ phase and optionally the β phase,                    in particular also comprises the β phase;                        the alloy of the top layer comprises at least 1% by weight aluminum (Al);        the alloy of the top layer (10) comprises at least 0.1% by weight,                    in particular comprises 0.3% by weight,            very particularly comprises between 0.1% by weight and 0.7% by weight, yttrium (Y);                        the content of cobalt (Co) in the alloy of the top layer is between 15% by weight-30% by weight,                    in particular is 18% by weight-27% by weight,            very particularly is between 21% by weight-24% by weight;                        the content of chromium (Cr) in the alloy of the top layer is between 12% by weight-22% by weight,                    in particular is between 15% by weight-19% by weight;                        the top layer contains the β phase,                    in particular at least 5% by volume;                        the top layer comprises an alloy consisting of nickel (Ni), cobalt (Co), aluminum (Al), chromium (Cr), tantalum (Ta) and optionally yttrium (Y),                    in particular consists thereof;                        the top layer comprises an alloy consisting of nickel (Ni), cobalt (Co), aluminum (Al), chromium (Cr), tantalum (Ta), iron (Fe) and optionally yttrium (Y),                    in particular consists thereof;                        the top layer comprises an alloy consisting of nickel (Ni), cobalt (Co), aluminum (Al), chromium (Cr), tantalum (Ta) and yttrium (Y),                    in particular consists thereof;                        the top layer comprises an alloy consisting of nickel (Ni), cobalt (Co), aluminum (Al), chromium (Cr), tantalum (Ta), iron (Fe) and yttrium (Y),                    in particular consists thereof;                        the alloy of the layers (7, 10) comprises no iron (Fe);        the proportion of iron (Fe) in the alloy of the top layer is between 0.5% by weight-5.0% by weight,                    in particular is between 1.0% by weight-4.0% by weight, and            very particularly is 2.7% by weight;                        the content of chromium (Cr) in the alloy of the top layer is between 12% by weight-16% by weight,                    in particular is 14.4% by weight;                        the proportion of aluminum (Al) in the alloy of the top layer is between 7% by weight-8% by weight,                    in particular is 7.75% by weight;                        the proportion of rhenium (Re) in the alloy of the top layer is 0.1% by weight-2% by weight;        the content of tantalum (Ta) in the alloy of the top layer is between 5% by weight and 6.8% by weight;        the alloy of the metallic layers contains no platinum (Pt);        the content of cobalt (Co) in the alloy of the top layer is between 11% by weight-14.5% by weight;        the content of chromium (Cr) in the alloy of the top layer is between 14% by weight-16% by weight;        the content of aluminum (Al) in the alloy of the top layer is between 9% by weight-13% by weight;        the content of yttrium (Y) in the alloy of the top layer is between 0.1% by weight-0.7% by weight;        the alloy of the top layer comprises between 4% by weight and 7.5% by weight,                    in particular comprises between 3.0% by weight and 6.0% by weight, tantalum (Ta);                        the content of tantalum (Ta) in the alloy of the top layer is between 3.5% by weight and 5.5% by weight,                    in particular is 4.5% by weight;                        the content of cobalt (Co) in the alloy of the top layer is between 21% by weight-25% by weight,                    in particular is between 22% by weight-23.5% by weight, very particularly is 23% by weight;                        the content of chromium (Cr) in the alloy of the top layer is between 18% by weight-22% by weight;        the top layer comprises no yttrium (Y)        the content of aluminum (Al) in the alloy of the top layer is between 8% by weight-12% by weight;        the content of yttrium (Y) in the alloy of the top layer is between 0.1% by weight-0.7% by weight;        the content of yttrium in the top layer is 0.2% by weight-0.6% by weight, in particular 0.3% by weight to 0.5% by weight, yttrium (Y).        
These measures listed above can be combined with one another as desired in order to achieve further advantages.